Conventionally, there is known a valve driving gear, for arbitrarily and automatically controlling a valve, so as to open or close the valve at a variable timing, according to a rotary speed of an engine, with an arrangement of a hydraulic valve rush adjuster between a dynamic-system valve and a valve operating cam, for a gasoline engine for a car, for example, in Japanese Unexamined Patent Publication No. 1-232103.
A pivot portion of the valve driving gear is configured as shown in FIG. 5. In other words, there is shown a cylinder head 51, a cam 52, and an intake valve 53 (its stem portion). Between the cam 52 and the intake valve 53, there is provided a bucket 54 in a plunger insertion hole 51a, of the cylinder head 51, so as to be slidable, and a hydraulic valve rush adjuster 55 inside the bucket 54. With a rotation of the cam 52, the intake valve 53 is actuated for up-and-down strokes, through the bucket 54 and the hydraulic valve rush adjuster 55, so that the valve is opened or closed.
The hydraulic valve rush adjuster 55 forms a plunger 58 with a first adjuster portion 55A, which forms a middle-pressure chamber 56, positioned in the upper side, and two sets of adjuster members of a second adjuster portion 55B, which forms a high-pressure chamber 57, positioned in the lower side.
The first adjuster portion 55A comprises a first adjuster body 59A, a first valve spring 60, a first check ball 61, a first return spring 62, and a first check valve case 63.
The second adjuster portion 55B comprises a second adjuster body 59B, a second valve spring 64, a second check ball 65, a second return spring 66, and a second check valve case 67.
The first and second check balls 61 and 65 allow oil to flow from an oil reserve chamber 68 (described later) into the first and second adjuster bodies 59A and 59B, but do not allow it to flow out of the adjuster bodies.
The inside of the bucket 54, and a guide member 69, for guiding the above plunger 58, form the oil reserve chamber 68. This oil reserve chamber 68 has communication with an oil passage 71 of the cylinder head 51 through an oil inlet 70, provided in the side portion of the bucket 54, and has communication with the interior of the first and second adjuster bodies 59A and 59B through an oil outlet 72, provided on an inner wall of the top of the bucket 54.
Oil from the oil passage 71, of the cylinder head 51, is supplied to the oil reserve chamber 68, and then is necessarily supplied to the middle-pressure chamber 56, through the first check ball 61, from the interior of the first adjuster body 59A. The oil in the middle-pressure chamber 56 is supplied to the high-pressure chamber 57, through the second check ball 61, from the interior of the second adjuster body 59.
A volumetric rate regulation spring 73 is formed by two springs, an inner spring 74 and an outer spring 75, which have a considerably strong spring force (high hardness) relative to the first return spring 62, and is used so that a volume of the middle-pressure chamber 56 is always maintained at a fixed value, while the intake valve 53 is seated.
Next, an operation of this construction will be explained. The hydraulic valve rush adjuster 55, between the intake valve 53 and the cam 52, runs with two sets of adjuster members of the first adjuster portion 55A and the second adjuster portion 55B, which are combined to operate with each other. While an oil leak amount from the high-pressure chamber 57, of the second adjuster portion 55B, is set to a value smaller than an oil leak amount from the middle-pressure chamber 56, of the first adjuster portion 55A, a spring force of the second return spring 66, of the second adjuster portion 55B, is set to a value greater than a spring force of the first return spring 62. In other words, the hydraulic valve rush adjuster 55, which is provided between the cam 52 and the intake valve 53, to be opened by the cam 52 and intended for automatically adjusting a valve rush of the intake valve 53, adjusts oil leak amounts of respective oil chambers 56 and 57, in the side of the second adjuster portion 55B, when the cam 55 is running to values smaller than those in the side of the first adjuster portion 55A, by means of two sets of the adjuster members, the first adjuster portion 55A having the middle-pressure chamber 56 and the second adjuster portion 55B having the high-pressure chamber 57, which are provided with different properties.
This makes it possible to realize accurate dynamic properties, which determine an initial sinking amount in the first adjuster portion 55A, and to realize static properties in the second adjuster portion 55B, having an less oil leak amount. In addition, the spring force of the second return spring 66 is greater than the spring force of the first return spring 62, and therefore an initial volume of the middle-pressure chamber 56 is set very accurately, and a fluctuation of an initial value is reliably absorbed. It is described that, therefore, valve timing can be arbitrarily and automatically controlled with variable settings according to a rotary speed of the engine.
This case of the conventional engine valve driving gear, however, has the following problems:
(1) This engine valve driving gear is a gasoline engine for a car, having the hydraulic valve rush adjuster 55 between the cam 52 and the intake valve 53, to be opened by the cam 52. The gasoline engine for a car has a speed fluctuation from low to high speeds. Therefore, the valve timing is arbitrarily and automatically controlled with variable settings according to the rotary speed of the engine.
Accordingly, the hydraulic valve rush adjuster 55 is operated by two sets of adjuster members, the first adjuster portion 55A (in the cam side) and the second adjuster portion 55B (in the valve side) being combined with each other for the operation. In other words, the hydraulic valve rush adjuster 55, for automatically adjusting a valve rush of the intake valve 53, adjusts oil leak amounts of respective oil chambers 56 and 57 in the second adjuster portion 55B when the cam 55 is running to values smaller than those in the first adjuster portion 55A, by means of two sets of the adjuster members, the first adjuster portion 55A having the middle-pressure chamber 56 and the second adjuster portion 55B having the high-pressure chamber 57, which are provided with different properties.
The oil leak amount, however, depends upon an oil viscosity and a gap (first and second oil leak passages). In other words, the oil viscosity depends upon an oil service temperature during operation and, as to gaps, it is difficult to manage the unevenness of a dimensional accuracy of components in the hole side and in the shaft side, and therefore, the oil leak amount is not fixed. Furthermore, this valve driving gear is operated by two sets of adjuster members, the first adjuster portion 55A and the second adjuster portion 55B, in which the hydraulic valve rush adjuster 55 has a large number of components in a complicated construction.
(2) In recent years, there has been used a generator and a cogeneration system (an apparatus for supplying hot-water and electricity) driven by a diesel engine. A rotary speed of an engine used for this product is different from the rotary speed of the engine for a car. It does not have a speed variation from a low speed to a high speed, and it is always running at a fixed rotary speed.
On the other hand, as a countermeasure for an improvement of increased power and exhaust gas properties, it is necessary to increase a lift of the intake valve 53 of the valve mechanism, at a high-speed rated output, in order to increase its operating angle and to decrease its effective compression ratio (cylinder volume/compression volume), in order to improve a performance of power and exhaust gas properties, so as to suppress the pressure in the cylinder. In addition, at engine start, it is necessary to decrease the lift of the intake valve 53 in order to decrease its operating angle and to increase its effective compression ratio, in order to improve its engine start properties. In other words, it is required to have variable operating angles and effective compression ratios of the intake valve 53 during high-speed running and at engine start.
A control and apparatus for controlling an engine valve mechanism which satisfies these quality requirements and has a simple construction is greatly needed.